I was driving the other day, with my 3 children in the car and I was at a stop sign. When I turned my steering wheel wouldn't turn and I had to stop to avoid going into oncoming traffic. Luckily the guy coming up to the side of my car was able to stop and I reversed back to the stop sign. I put the car back into drive and it worked fine after that. I checked my power steering fluid and it is full. I'm not sure what's going on but I am afraid to drive it now. What could it be?